CROSSLINKABLE COATING COMPOSITIONS

Abstract: A crosslinkable liquid carrier-based coating composition formulated from components comprising an organic polymer(s) having acetoacetyl group functionality, a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, and a non-polymeric monoacetoacetyl compound(s) which can evaporate on coating formulation selected from at least one of alkyl acetoacetate, alkyl acetoacetamide and 1-alkyl-1,3-butanedione where said alkyl groups in said compounds have from 1 to 3 carbon atoms, and wherein the ratio of the number of acetoacetyl groups from said monoacetoacetyl compound(s) to the number of polymer-bound acetoacetyl groups from said organic polymer(s) having acetoacetyl group functionality is within the range of from 0.8/1 to 1.5/1. The preferred monoacetoacetyl compound is methyl acetoacetate.

Description: CROSSLINKABLE COATING COMPOSITIONS The present invention relates to crosslinkable liquid carrier- based coating compositions in which the basis of the crosslinkability is provided by the reaction in an applied coating between the functional groups of an acetoacetyl-functional polymer and a polyamine used in the formulation of the compositions. The provision of polymeric coatings from coating compositions for use on a variety of substrates for various purposes (eg, protective, decorative, adhesive or sealant purposes) is well known. It is also well known to improve the performance of such coatings by causing them to become crosslinked (cured) after coating film formation from the composition. For this purpose it is known to employ crosslinkable coating compositions whereby the composition includes components which react to cause crosslinking when a coating is formed from the composition - such as a polymer having reactive functional groups and a coreactant material (which could e.g. be a non-polymeric or oligomeric material or another polymer) having 2 or more groups reactable with those of the functionalised polymer. Such reaction (to cause crosslinking) is of course not intended to take place to any unacceptable degree until actual coating from the composition is effected. As might be imagined, many such coating compositions have a very short pot-life, i.e. a very short period of time before unacceptable premature crosslinking occurs in the composition (as manifested by a very large increase in viscosity and subsequent gelation) . Consequently, it may be necessary with such coating compositions to employ them for coating very quickly after they have been prepared from their individual constituents. A potentially useful and known class of coating compositions comprise an acetoacetyl-functional polymer and a polyamine. Such compositions are described, e.g. in Journal of Coating Technology, Vol. 61 (771) pages 31-37, 1989, and also in Journal of Paint Technology, Vol. 46, No. 591, April 1974, pages 70-75, and it is postulated that crosslinking occurs by means of enamine formation between the enolic acetoacetyl groups and the amine groups. Such compositions can be aqueous-based and non aqueous liquid-based. The problem with such compositions, however, is that their working pot- life is extremely short, being of the order of a few minutes to a few hours before premature crosslinking and gelation occurs. It has been proposed to increase the po -life of compositions of this type by blocking the amine groups of the polyamine with a ketone or aldehyde to form corresponding ketimine or aldimine compounds prior to mixing with the acetoacetyl-functional polymer; examples of such compositions are disclosed in US Patent 4772680. On coating formation, exposure to adventitious moisture results in regeneration of the free amine groups which are then available to effect crosslinking. Nevertheless such compositions also have their disadvantages. The ketimine or aldimine group is very moisture sensitive and as such water must, in practice, be rigorously excluded from the stored compositions. This can result in problems when using pigmented systems: thus pigments normally tend to be wet or hydrated, and such products would therefore prematurely trigger the amine deblocking; therefore anhydrous pigments are required - but this in turn begets other problems such as how to effectively employ anhydrous pigments such that they will not absorb moisture; anhydrous pigments are also more expensive. In addition to this, there is a very limited choice of commercially available suitable ketimines or aldimines for use as the hardener. To widen this choice it would be necessary to effect a prior ketimation or aldimation of an amine oneself, thereby incurring unwelcome additional expense. In practice, therefore, the use of such a system may restrict the choice of available coreactant (hardener) for the acetoacetyl-functional polymer, even though there is a very wide range of suitable commercially available unblocked (free) polyamines . It is disclosed in passing by Witzeman et al, Polym. Mater. Sci. and Eng., £5., 1000-1006 (1990) that the pot life of compositions containing acetoacetyl-functional polymer and polyamine may be significantly extended by the addition of monoacetoacetyl compounds such as methyl acetoacetoacetate to the composition. However, Witzeman et al also state that the use of such an expedient causes the ultimate properties of the system to suffer, implying that it is not a viable way forward to achieve extended pot life is such compositions. We have now discovered novel liquid carrier-based coating compositions formulated from acetoacetyl-functional polymers and free (i.e. unblocked) polyamines which not only have an acceptable working pot-life (as good as or better than the blocked amine-containing compositions described above), but are not sensitive to moisture. In addition to this they provide applied coatings which often have an acceptable rate of ambient or low temperature cure. Yet further, the coatings derived therefrom possess excellent properties, such as good solvent resistance, hardness, and good resistance to weathering and good saltspray performance. According to the present invention there is provided a crosslinkable liquid carrier-based coating composition formulated from components comprising an organic polymer(s) having acetoacetyl group functionality, a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, and a non-polymeric monoacetoacetyl compound(s) which can evaporate on coating formation selected from at least one of alkyl acetoacetate, alkyl acetoacetamide and 1-alkyl-l,3-butanedione where said alkyl groups in said monoacetoacetyl compounds have from 1 to 3 carbon atoms, and wherein the ratio of the number of acetoacetyl groups from said monoacetoacetyl compound(s) to the number of polymer-bound acetoacetyl groups from said organic polymer(s) having acetoacetyl group functionality is within the range of from 0.8/1 to 1.5/1. It is particularly noteworthy that coatings derived from the invention compositions show improved weathering in comparison to coatings derived from corresponding compositions which however lack the monoacetoacetyl compound. There is also provided according to the invention a method of preparing a crosslinkable liquid carrier-based coating composition which method comprises formulating components which comprise an organic polymer(s) having acetoacetyl functionality,a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, and a non-polymeric monoacetoacetyl compound(s) which can evaporate on coating formation selected from at least one of alkyl acetoacetate, alkyl acetoacetamide and 1-alkyl-l,3-butane dione where said alkyl groups in said acetoacetyl compounds have from 1 to 3 carbon atoms, wherein the ratio of the number of acetoacetyl groups from said monoacetoacetyl compounds (s) to the number of polymer-bound acetoacetyl groups from said organic polymer(s) having acetoacetyl group functionality is within the range of from 0.8/1 to 1.5/1. There is further provided according to the invention the use of a coating composition as defined supra for the provision of a crosslinked coating on a substrate. There is yet further provided according to the invention a crosslinked coating derived from a coating composition as defined supra. Thus the compositions of the invention incorporate a volatile monoacetoacetyl compound, such as methylacetoacetate, in a crosslinkable composition containing an organic polymer and a polyamine as disclosed in Witzeman et al, thereby significantly improving pot life. However, a critical feature of such compositions is that a selected range of the ratio of the number of acetoacetyl groups from the monoacetyl compound(s) in said composition to the number of polymer-bound acetoacetyl groups in said composition is employed, viz 0.8/1 to 1.5/1, which contrary to the teaching in Witzeman, allows a combination of extended pot life as well as the formation of coatings of unimpaired improved properties (i.e. in comparison to coatings derived from corresponding compositions of acetoacetyl functional polymers and polyamines not having a monoacetoacetyl compound incorporated therein) . Indeed, some properties of the resulting crosslinked coatings derived from the invention composition are actually significantly superior to those of coatings derived from corresponding compositions lacking the monoacetoacetyl compound - such as the resistance to the loss of gloss under accelerated ultra violet weathering conditions. The coatings derived from compositions of the invention retain gloss under accelerated QUV conditions for highly extended periods of time, while the coatings derived from corresponding compositions lacking the monoacetoacetyl compound lose their gloss almost immediately. If a ratio of acetoacetyl groups in the monoacetoacetyl compound to polymer-bound acetoacetyl groups below 0.8/1 is employed, no significant improvement of pot life is found. If a ratio above 1.5/1 is used, the properties of the resulting coatings may be impaired due to the cure rate being very slow leading to a low degree of cure. Preferably the ratio in within the range of from 0.8/1 to 1.2/1, more preferably 0.9/1 to l.l/l. The coating compositions of the present invention also provide several other advantages which are not enjoyed by the compositions of the prior art employing acetoacetyl-functional polymers and blocked polyamines (ketimines or aldimines) . For example, they can be derived using any suitable polyamine hardener, which does not need to be blocked prior to incorporation into the composition. They are not sensitive to moisture and consequently no special precautions need to be taken in this regard during storage; also they are equally suited to providing conventionally pigmented (i.e. using conventional non-anhydrous pigments) and clear coatings. Additionally, as mentioned above, they possess excellent pot-life and are often suitable for ambient temperature or slightly elevated temperature curing, although of course higher temperature curing can also be effected if appropriate. The stability of the invention compositions is such that they may even as an option incorporate acids (such as benzoic acid) to improve the efficiency of the cure reaction between the polymer-bound acetoacetyl groups and the polyamine after coating formation. Acids are known to catalytically accelerate such crosslinking so the resource of being able to include acids in the invention composition without ruining pot life is most surprising. The compositions of the invention may be organic liquid- based or they may be water-based. By an organic liquid-based coating composition is meant a composition in which the components are carried in a liquid medium of which at least one organic liquid is the principle component (greater that 50 wt. % of the carrier medium say, and more usually at least 80 wt. %) ; minor quantities of water may optionally be present. By an aqueous-based coating composition is meant a composition in which the components are carried in a liquid medium of which water is the principle component (greater than 50 wt. % of the carrier medium say, and more usually at least 80 wt.%); minor quantities of organic liquid(s) may optionally be present. . In the compositions of the invention, one or more or all of the acetoacetyl functional polymer, the polyamine and the monoacetoacetyl components may be dissolved in the liquid carrier medium, and in the case of organic liquid-based compositions it is not uncommon for all three types of component to be dissolved therein. If a component is not truly dissolved in the liquid carrier medium it may alternatively be dispersed in the liquid carrier medium, i.e. exist in the form of a dispersion of non-solubilized particles or droplets (depending on whether it is a solid or liquid) rather than as properly solubilized material. Thus, the acetoacetyl-functional polymer could e.g. be present in the form of colloidally dispersed particles (i.e. in latex form) , while the polyamine and monoacetoacetyl compounds could be present in the form of colloidally dispersed particles or droplets (depending on whether they are in solid or liquid form) . Thus, one or more or all of the acetoacetyl functionalized polymer, the polyamine and the monoacetoacetyl components may be dispersed (rather than dissolved) in the liquid carrier medium. It would also be possible for a component of the composition to itself provide at least part of the liquid carrier medium - if it were a liquid with suitable characteristics for a carrier medium as might be the case with some polyamines and were present in a large enough quantity. In the compositions of the invention it is preferred that the ratio of the number of acetoacetyl groups of the acetoacetyl functional polymer(s) to the number of acetoacetyl-reactive amino groups of the polyamine compound(s) is within the range of from 0.5/1 to 2/1 more preferably from 0.8/1 to 1.5/1, in order to achieve the best possible cure rates. A ratio at or very near to 1 is particularly preferred (say 0.9/1 to l.l/l) . By a polymer-bound acetoacetyl group in this specification is meant a group having the formula where the methyl group may optionally be mono, di or tri-substituted (for example so as to provide therewith a higher alkyl group of 2 to 10 carbon atoms, usually 2 to 4 carbons atoms), and the methylene group may optionally be monosubstituted (usually by alkyl of 1 to 4 carbon, particularly methyl) . The methyl group could also, in principle, be replaced by a cyclic hydrocarbyl group (optionally substituted) such as an optionally substituted phenyl group or an optionally substituted heterocyclic group, and the resulting alternative groupings are also considered to be acetoacetyl groups for the purpose of this specification. A polymer-bound acetoacetyl group will normally be provided in the environment of an acetoacetate grouping of formula: 0 0 CH 3 - ICI-CH 2 - ICI-0- (2) or an acetoacetamide grouping of formula: 0 O R 1 CH 3 -C II-CH 2 - ICI-IN- (3) or a 1,3 diketone grouping of formula: CH,-C i-CH,- ϊCl-R,- (4) where R is hydrogen or a monovalent hydrocarbyl radical such as an (optionally substituted) alkyl, aryl, aralkyl or alkaryl radical 2 (usually of 1 to 10, particularly 1 to 6 carbon atoms) and R is a divalent hydrocarbyl radical such as an (optionally substituted) alkylene, arylene, aralkylene or alkarylene radical (usually of 1 to 20, particularly 1 to 10 carbon atoms) . It is preferred, however, that the polymer-bound acetoacetyl group is provided by an acetoacetate or acetoacetamide group, and more preferably by an acetoacetate group. By an acetoacetyl-reactive amino group is meant an amino group which will react with an acetoacetyl group to form a covalent bond between the compounds containing the groups . Such groups are normally acetoacetyl-reactive primary amino (-NH 2 ) and/or secondary amino (-NH-) groups. In the particular context of this specification, we are including acetoacetyl-reactive nitrogen bound -NH 2 groups (such as in the hydrazino grouping -NHNH 2 ) as examples of amino groups as well as the more preferred carbon-bound acetoacetyl-reactive amino gro Turning now specifically to the acetoacetyl-functional polymer. There are two basic approaches to the preparation of such polymers. In the first approach (A) , an acetoacetyl-functional mononomer is polymerised, usually with other comonomer(s) (not having acetoacetyl groups) to directly form a polymer having acetoacetyl groups. In the second approach (B) , a precursor polymer is first formed having acetoacetylatable precursor groups, and at least a proportion of these precursor groups are then converted to acetoacetyl groups using an appropriate acetoacetylating reagent. The acetoacetyl groups can be disposed laterally (i.e. being chain pendant) and/or terminally although they will usually be disposed at least laterally. The acetoacetyl group content of the polymer will generally be within the range of from 1 to 60% by weight of the polymer, more usually 3 to 50 weight %. The number average molecular weight (Mn) of the acetoacetyl-functional polymer can vary between wide limits, but will generally be within the range of from 300 to 10 s g mole "1 . Polymers in aqueous dispersion, prepared by emulsion polymerisation are likely to have a different Mn range (say 1000 to 10 6 g mole "1 ) to organic liquid- soluble polymers (say 500 to 100,000 preferably 750 to 50,000 g mole "1 ) . The polymer of either approach A or approach B could be an addition polymer derived from one of more olefinically unsaturated monomers (using free-radical initiation for example) ; such a polymer is herein called an "olefinic polymer" for convenience. It could also be an addition polymer derived from monomers which are not olefinically unsaturated such as, in particular a polyurethane polymer (or an analogue thereof such as a polyurea) . It could also be a condensation polymer such as, in particular, a polyester polymer (and in fact it is preferred to use approach B in order to make acetoacetyl-functional polyesters and polyurethanes) . Looking first at olefinic acetoacetyl-functional .polymers. These may be made using approach A or approach B as mentioned above. When using approach A, one polymerises an olefinically unsaturated monomer(s) bearing one or more acetoacetyl groups optionally (but preferably) in conjunction with one or more other olefinically unsaturated monomers copolymerisable therewith. Examples of suitable acetoacetyl-functional olefinic monomers include acetoacetic esters and amides of hydroxyalkyl (meth)acrylates (where the alkyl is usually of 1 to 5 carbon atoms) or allyl alcohol, specific examples of which include the acetoacetic esters and amides of hydroxymethyl (meth)acrylate, hydroxyethyl (meth) acrylate, and hydroxypropyl (meth) acrylate. Examples are acetoacetoxyethyl acrylate and acetoacetoxyethyl methacrylate. Others include allyl acetoacetate and vinyl acetoacetate. Non acetoacetyl-functional olefinic monomers include dienes such as 1,3- butadiene, isoprene and chloroprene, styrene, alpha-methyl styrene, divinyl benzene, vinyl toluene, acrylamide, methacrylamide, acrylonitrile, methacrylonitile, vinyl halides such as vinyl chloride and vinylidene chloride, vinyl esters such as vinyl acetate, vinyl propionate and vinyl laurate, vinyl trimethoxy silane, heterocyclic vinyl compounds, olefinically unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid, (or their anhydrides) , and acrylic or meth acrylic esters of mono-, di- or polyfunctional hydroxyl compounds (usually of 1 to 20 carbon atoms) such as methyl (meth) acrylate, ethyl (meth)acrylate, hydroxyethyl (meth)acrylate, n-propyl (meth)acrylate, hydroxypropyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and isobornyl (meth)acrylate. When using approach B, one polymerises an olefinically unsaturated monomer(s) bearing one or more acetoacetylatable precursor groups, particularly hydroxyl (although thiol and amino groups e.g. can also be used in principle) , optionally (but preferably) in conjunction with one or more other olefinically unsaturated monomers copolymerisable therewith (not bearing acetoacetylatable precursor groups) , to form a precursor olefinic polymer. The acetoacetylatable groups of the precursor polymer are then converted, at least in part, to acetoacetyl groups using an acetoacetylating agent, such as diketene or (via transesterification) a lower alkyl (e.g. C1-C5) ester of acetoacetic acid, such as methyl acetoacetate, ethyl acetoacetate or (in particular) t-butyl acetoacetate. Examples of suitable olefinically unsaturated monomers not bearing acetoacetylatable precursor groups may be selected from the list given above for the olefinic polymers made using approach A (excluding acetoacetylatable group-containing monomers in this list of course) . Generally speaking, acetoacetyl-functional olefinic addition polymers, whether made by approaches A or B, will contain 0.5 to 100 weight % (more preferably 1 to 50 weight %) of monomer units bearing acetoacetyl groups and 0 to 99.5 weight % (more preferably 50 to 99 weight %) of monomer units not bearing acetoacetyl groups (which could of course, in approach B, include monomer units bearing precursor acetoacetylatable groups which remain after an incomplete acetoacetylation) . Such olefinic addition polymers often usefully have an acetoacetyl group content of 1 to 50 weight % and a glass transition temperature Tg of from -40 to 100°C. Number average molecular weight (Mn) is usually within the range of 1000 to 10 s g mole "1 . Hydroxyl number is usually from 0 to 200 mg KOH/g. The techniques for the preparation of olefinic addition polymers are extremely well known in the prior art and need not be described here in detail. Suffice to say that they usually employ a free-radical initiated polymerisation process using a free-radical- generating initiator with (usually) appropriate heating or irradiation being employed. While solution polymerisation in an organic solvent may be employed, such polymerisations are often effected in an aqueous medium and in particular aqueous emulsion polymerisation is often used to prepare an aqueous latex of the polymer with conventional dispersants and initiators being employed. Such a latex could be used "as is" for a composition of the invention or isolated from the aqueous medium before incorporation into the composition. Turning now to condensation acetoacetyl-functional polymers, and more particularly polyester polymers. Using approach B to prepare such polyesters, which is preferred, one uses a monomer component (s) in the synthesis thereof which will provide acetoacetylatable precursor groups in a precursor polymer, particularly hydroxyl groups (although thiol and amine groups e.g. could in principle also be used) , and then the precursor groups are converted at least in part to acetoacetyl groups using an appropriate acetoacetylating agent such as diketene or (via transesterification) a lower alkyl (e.g. Cl to C5) ester of acetoacetic acid, such as methyl acetoacetate, ethyl acetoacetate and (in particular) t-butyl acetoacetate. Thus, it is well known that polyesters, which contain carbonyloxy (i.e. -C(=0)-0-) linking groups may be prepared by a condensation polymerisation process in which an acid component (including ester-forming derivatives thereof) is reacted with a hydroxyl component. The acid component may be selected from one or more polybasic carboxylic acids such as di-or tricarboxylic acids or ester-forming derivatives thereof such as acid halides, anhydrides or esters. The hydroxyl component may be one or more polyhydric alcohols or phenols (polyols) such as diols, triols, etc. The reaction to form a polyester may be conducted in one or more stages (as is well known) . It would also be possible to introduce in-chain unsaturation into the polyester by employing as part of the acid component an olefinically unsaturated dicarboxylic acid. When preparing an acetoacetyl-functional polyester using approach B, a precursor polyester having acetoacetylatable precursor groups is first formed as mentioned above. This may be achieved by including an appropriate polyol(s) having two or more hydroxyl groups per molecule in the polyester synthesis. (If only a polyol(s) with two hydroxyl groups were used, i.e. a diol, it would of course be necessary to use a stoichiometric excess in relation to the acid component to ensure that the resulting precursor polyester was hydroxyl-terminated and therefore had acetoacetylatable precursor hydroxyl groups. It is therefore better to also include a polyol(s) with 3 or more hydroxyl groups as part of the hydroxyl component in order to provide lateral hydroxyl groups in the resulting polyester; the presence of terminal hydroxyl groups would therefore then be optional, although one could still have terminal as well as lateral hydroxyl groups if desired) . There are numerous carboxylic acids (or their ester forming derivatives) which can be used in polyester synthesis for the provision of the acid component. One can eg mention C4 to C20 aliphatic, alicyclic and aromatic dicarboxylic acids (or higher functionality acids) or their ester-forming derivatives (such as anhydrides, acid chlorides, or lower alkyl esters) . Specific examples include adipic acid, fumaric acid, maleic acid, succinic acid, itaconic acid, sebacic acid, nonanedioic acid, decanedioic acid, 1,4- cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2- cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, and tetrahydrophthalic acid. Anyhydrides include succinic, maleic, phthalic and hexahydrophthalic anhydrides. Similarly there are numerous polyols which may be used in polyester synthesis for the provision of the hydroxyl component. The polyol(s) preferably have from 2 to 6 (2 to 3) hydroxyl groups per molecule. Suitable polyols with two hydroxy groups per molecule include diols such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), the 1,2-, 1,3-, and 1,4-, cyclohexanediols and the corresponding cyclohexane dimethanols, diethylene glycol, dipropylene glycol, and diols such as alkoxylated bisphenol A products, e.g. ethoxylated or propoxylated bisphenol A. Suitable polyols with three hydroxy groups per molecule include triols such as trimethylolpropane (1,1,1-tris (hydroxmethyl) ethane) . Suitable polyols with four or more hydroxy groups per molecule include pentaerythritol (2,2-bis (hydroxymethyl) - 1,3-propanediol) and sorbitol (1,2,3,4,5,6-hexahydroxyhexane) . The precursor polyester polyols often usefully have a Mn within the range 300 to 5,000 g mole "1 , a Tg within the range -40 to 120°C, a hydroxyl number of 30 to 250 mg KOH/g (preferably 80 - 150 mg KOH/g) , and an acid value of 0 to 50 mg KOH/g (preferably 0 - 30, particularly 4-25 mg KOH/g) . After acetoacetylation, the acetoacetyl content of the polymer is usually within the range of from 3 to 50 weight % and the acetoacetylated polyester polymers often usefully have a Tg within the range of -40 to 120°C. Mn is usually within the range of 400 to 5,500 g mole "1 . Hydroxyl number is usually within the range 0 to 150 mg KOH/g. The specific polymerisation techniques for making polyesters are extremely well known and need not be described here in detail. Suffice to say that they are usually carried out in the melt using catalysts such as tin-based catalysts and with the provision for removing any water (or alcohol) formed from the condensation reaction. Looking now (briefly) at acetoacetyl-functional polyurethane polymers (and their analogues such as polyurea polymers) . As is well known, polyurethane polymers (or analogous polymers such as polyureas) are generally made by reacting an organic polyisocyanate with an organic compound containing at least two isocyanate-reactive groups, particularly a macropolyol with the optional inclusion of a low molecular weight polyol. A favoured route to their formation includes the formation of an isσcyanate-terminated prepolymer followed by chain-extension with an active hydrogen containing compound. When using approach B to form an acetoacetyl-functional polyurethane, one could first form a precursor polyurethane polymer having precursor acetoacetylatable groups (particularly hydroxyl groups) by using an appropriate reagent in the polyurethane synthesis, e.g. a polyol with 3 or more hydroxyl groups to provide at least lateral precursor hydroxyl groups. When using the chain-extension route, such a reagent could be used in the prepolymer formation or in the chain-extension step. One could then convert at least a proportion of the precursor groups to acetoacetyl groups (as described above for olefinic polymers and polyesters) . (It would of course be possible to use only polyol (s) with 2 hydroxyl groups in the polyurethane polymer synthesis, provided that one ensured that the resulting polymer was hydroxyl-terminated - so allowing the preparation of an acetoacetyl group-terminated polyurethane polymer) . (One could of course have a polyurethane polymer with both terminal and lateral acetoacetyl groups) . It may be mentioned that acetoacetyl-functional condensation polymers, such as polyesters, and non-olefinic addition polymers, such as polyurethanes, may often usefully be used in the composition in the form of an aqueous dispersion (e.g. an aqueous latex) as well as in the form of an organic liquid solution. When using approach B for the synthesis of an acetoacetyl- functional polymer, the conversion of the precursor groups (usually hydroxyl as mentioned above) to acetoacetyl groups is usually effected such that at least 30% of such groups are converted to acetoacetyl groups, and more preferably 50 to 100% of the precursor groups are so converted. Acetoacetyl-functional polymers are quite well known, and for more specific information as to their preparation one may refer to patent references such as US Patents 4772680 and 4408018, and journal articles such as Journal of Coating Technology, Vol 61, No. 771, April 1989 (pages 31 to 37) and Journal of Coating Technology, Vol 62, No 789, October 1990 (pages 101 to 112) . It may be mentioned that such polymers can be made water- dispersible, water-soluble or water-reducible (if necessary) , by arranging for suitable lateral ionic and/or nonionic groups to become incorporated into the polymeric structure as a result of using appropriate monomers in the polymer synthesis. Examples of such groups include ionic groups such as carboxylate or sulphonate groups (made e.g. by neutralizing polymer-bound carboxyl or sulphonic acid groups in the polymer) and nonionic groups such as polyoxyethylene oxide chain-containing groups. Such a resource is well known in the art. It would be possible to use in-chain polyoxyethylene oxide groups to achieve or enhance water-solubility, dispersibility or reducibility. Turning next to the polyamine(s) component of the composition of the invention. Such materials can in principle be low molecular weight or monomeric materials, oligomeric materials or polymeric materials. The polyamine may e.g. have primary and/or secondary amino groups and have from 2 to 10 (more often 2 to 6) such amino groups per molecule, and (usually) 2 to 200 carbon atoms. Suitable examples of polyamines with 2 such amino groups per molecule include diamines such as ethylenediamine, propylenediamine, butylenediamine, pentamethylenediamine, hexa ethylenediamine, decamethylenediamine, 4,7-dioxadecane-l,10-diamine, dodecamethylenediamine, 4,9-dioxadodecane-l,12-diamine, 7-methyl-4,10- dioxatridecane-1,13-diamine, 1,2-diaminocyclohexane, 1,4- diaminocyclohexane, 4,4' -diaminodicyclohexyl methane, isophoronediamine, bis (3-methyl-4-aminocyclohexyl)methane, urea, 2,2- bis (4-aminocyclohexyl)propane, 3-amino-l- (methylamino)propane, 3- amino-1- (cyclohexylamino)propane and N- (2-hydroxyethyl) ethylenediamine. Suitable polyamines with 3 such amino groups per molecule, include polyamines such as tris (2-aminoethyl)amine, bis (3- aminopropyl)methylamine, melamine and products of the JEFFAMINE (Registered Trade Mark) series represented by the formula: where E is the residue of an aliphatic triol and x, y and z are integers the sum of which is from 5 to 85 (this may not be a whole number if the product is a mixture of compounds with differing x, y and/or z) . Other suitable polyamines with from three to ten amino groups per molecule are polyalkylene polyamines represented by the formula: H 2 N (rR 2 -NH) 5 R 4 — NH 2 (6) where the group R 4 and the n groups R 3 which may be the same or different, are (cyclo) alkylene groups of from 1 to 6 (and preferably from 1 to 4) carbon atoms, and n is an integer from 1 to 8 and preferably from 1 to 4. Examples of polyamines of formula (6) are diethylenetriamine, dipropylenetriamine and dibutylenetriamine. Other suitable polyamines which could be used include the adducts of an amino compound with a polyfunctional epoxy, isocyanate, maleinate, fumarate or (meth) acryloyl compound, such that the resulting material has two or more amino groups (primary or secondary) per molecule. Many examples of such polyamines are disclosed in US Patent 4772680 reference to which is incorporated herein. It would also be possible to employ as the polyamine compound, polyhydrazides such as those dicarboxylic acid bishydrazides of formula H,N-NH-C(0) -R 5 -C(0) -NH-NH, (7) where R s is a covalent bond or a polyalkylene (preferably polymethylene) or alicyclic group having from 1 to 34 carbon atoms. Examples of suitable dihydrazides include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, cyclohexane dicarboxylic acid bis-hydrazide, azelaic acid bis-hydrazide, and sebacic acid dihydrazide. The polyamine compound could also in principle be an organi polymer with an average of at least 2 acetoacetyl-reactive amino groups per molecule, such as an olefinic polymer, a polyester polymer or a polyurethane polymer, having lateral and/or terminal amino groups (more usually at least lateral amino groups) . Such a polymer is, in particular an olefinic polymer bearing at least lateral amino groups. An olefinic polymer bearing chain-pendant (lateral) amine functionality is preferably a copolymer formed by first preparing, using a free-radical-initiated polymerisation process, a precursor copolymer comprising polymerised units of at least one olefinically unsaturated monomer having an amine precursor group(s) (i.e. a group which may be subsequently reacted to provide a pendant amine group) and at least one other olefinically unsaturated monomer (i.e. a monomer which does not provide an amine precursor group) , and subsequently reacting at least a proportion of the amine precursor groups to provide chain-pendant amine functional groups. The chain-pendant amine functionality can, if desired, be introduced into the olefinic polymer by an imination reaction involving the carboxyl (or carboxylate salt) groups of a precursor polymer and an added aziridine compound. The aziridine compound is commonly referred to as an alkylene imine and preferably has the formula H I N \ H-C C-R 6 (8) I I where R s and R 7 which may be the same or different are selected from hydrogen, benzyl, aryl, and alkyl of 1 to 5 carbon atoms; and where R 8 is hydrogen or alkyl of 1 to 5 carbon atoms. More preferably R 6 is hydrogen, R 7 is hydrogen or alkyl of 1 to 5 carbon atoms (particularly methyl) and R 8 is hydrogen. Ethylene imine (R 6 = R 7 = R 8 = H) and propylene imine (R 6 = R 8 = H; R 7 = methyl) are particularly preferred aziridines because of their relatively low cost and ready availability. Corresponding chain-pendant amino ester groups (providing chain-pendant amine functional groups) formed by the imination reaction include those of formulae: 0O HH RR 66 0 R 6 H 1 1 I I - I cI - • o ■ - C - c - NH 2 ( 9 ) and - I CI 0 - C - C - NH 2 (10) 1 1 I I R 8 R 7 R 7 R 8 where R 6 , R 7 and R 8 are as defined above. The amount of alkylene imine used should be sufficient to iminate the desired proportion of the carboxyl groups to aminoalkyl ester groups. Preferably the amount used should be sufficient to iminate about 5% to 95%, preferably 20% to 80%, of the carboxyl groups on the precursor polymer. The imination technique is in itself well-known and may be performed by techniques known to the art. Monomers which can be used to provide carboxyl precursor groups in the precursor polymer are particularly monoolefinically unsaturated monocarboxylic acids and/or dicarboxylic acids, mostly of 3 to 6 carbon atoms, especially acrylic acid, methacrylic acid, beta- carboxyethylacrylate, fumaric acid and itaconic acid. Examples of olefinically unsaturated monomers which do not provide amine functional groups (or precursor groups thereof such as carboxyl groups) which may be mentioned include 1, 3-butadiene, isoprene, chloroprene, styrene, divinyl benzene, acryloniitrile, methacrylonitrile, vinyl halides (such as vinyl chloride and vinylidene chloride), vinyl esi-eir (such as vinyl acetate, vinylpropionate and vinyl laurate) , heterocyclic vinyl compounds, alkyl esters of monolefinically unsaturated dicarboxylic acids (such as di-n-butyl maleate and di-n-butyl fumarate) and, in particular, esters of acrylic acid and methacrylic acid of formula CH 2 = CR'COOR 10 (11) where R 9 is H or methyl and R 10 is alkyl or cycloalkyl of 1 to 20 carbon atoms (more preferably 1 to 8 carbon atoms) examples of which include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2- ethylhexyl methacrylate, isopropyl acrylate, isopropyl, methacrylate, n-propyl acrylate and n-propyl methacrylate. When used in aqueous-based compositions the polymeric polyamines will often be present as an aqueous dispersion of the polymer particles, and particularly in the form of an aqueous latex. Thus e.g. the polymeric amine could be prepared as an aqueous latex (using e.g. the imination reaction described above) and incorporated into the coating composition as such. The non-polymeric monoacetoacetyl compound which can evaporate on coating formation allows one to achieve an acceptable balance of improved pot-life and cure response and is selected from alkyl acetoacetate, alkyl acetoacetamide and 1-alkyl-l,3-butanedione where said alkyl is from 1 to 3 carbon atoms. The use of alkyl of more than 3 carbon atoms may not achieve a significant increase in pot life while the use of acetoacetic acid itself also results in fairly quick gelation. The methylene grouping in the acetoacetyl group in principle may optionally be appropriately monosubstituted, e.g. with methyl or ethyl. It will be noted that some of these materials, e.g. methyl acetoacetate and ethyl acetoacetate, were mentioned above as examples of materials which can be used to effect acetoacetylation (by transesterification) of a precursor polymer when preparing acetooacetyl-functional polymers using approach B (as discussed above) . The monoacetoacetyl compound is, in particular, selected from methyl acetoacetate and ethyl acetoacetate, with methyl acetoacetate being partic ar.j pr--.:erred. It may be mentioned here that additional to the advantages of the coating compositions discussed supra, the use of an acetoacetyl-functional polymer therein itself provides advantages which are independent of these other advantages. Thus an acetoacetyl- functional polymer will generally have a lower solution viscosity in comparison to the corresponding non acetoacetylated polymer at a given solids content, thereby allowing the use of less organic liquid in organic liquid-based compositions in which the components are dispersed or dissolved, or in other words allows a composition with a comparatively higher solids content. In such compositions the acetoacetyl groups of the polymer also enhances polymer solubility in the organic liquid carrier. In water-based compositions, based e.g. on condensation polymers such as polyesters or on non-olefinic addition polymers such as polyurethanes, the acetoacetyl groups of the polymer facilitates emulsification of the polymer, thereby improving its dispersion in the composition (although of course the polymer could also have groups for imparting water-emulsifiability or even water-solubility as discussed above) . The liquid carrier medium of the composition of the invention will be comprised at least in part (and usually at least predominantly) by an organic liquid(s) or by water. Examples of organic liquids, in many cases acting as a solvent for all the components, include aliphatic or aromatic hydrocarbons such as xylene and toluene, esters such as ethyl acetate, ethers, alcohols and nitroalkanes such as nitropropane. In the case of organic liquid-based compositions, the organic liquid carrier medium could in one embodiment be provided by a liquid organic plasticiser material such that the coating composition of the invention is in the form of a plastisol. (A plastisol is a nonaqueous fluid composition, ranging in viscosity from a pourable liquid to a heavy paste, which contains at least one particulate polymer, e.g. an olefinic polymer such as an acrylic polymer, dispersed in a non-volatile liquid organic plasticiser material which is compatible with the polymer. Under ordinary conditions of storage (ambient temperature) the polymer does not dissolve to any appreciable extent in the plasticiser but on heating the plastisol composition at an appropriate: -__evεted temperature, after forming a coating on a substrate, the plastisol composition gels to form a homogeneous coalesced mass which retains its homogeneous character permanently on cooling) . Examples of organic plasticiser materials include dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, dioctyl adipate, diisodecyl adipate, butyl benzyl phthalate, dibutoxyethyl phthalate, octylbenzyl phthalate and diisoheptyl phthalate. The plastisols may, and usually do, contain other materials, particularly inorganic fillers such as calcium carbonate, silica, talc, bentonite, glass powder, alumina, titanium dioxide and carbon. The coating compositions of the invention usually have a non-volatiles content within the range of from 25 to 100 weight %, more usually 40 to 85 weight %. (However, in the case of an aqueous dispersion the upper limit of non-volatiles content attainable is generally lower, e.g. 70 weight %) . (By non-volatiles are meant solids and/or non-volatile liquids such as might be provided by some low molecular weight polymers) . The components of the composition may be brought together in any appropriate manner or order using any suitable mixing technique. For example: the acetoacetyl-functional polymer and monoacetoacetyl compound may first be mixed together, and the polyamine then admixed therewith; or the acetoacetyl-functional polymer, the monoacetoacetyl compound and the polyamine may all be mixed together in a single stage; or the monoacetoacetyl compound and the polyamine may first be mixed together, and the acetoacetyl-functional polymer then admixed therewith. Once formulated, the composition is often storage-stable for a considerable period of time, e.g. 3 weeks up to one year or more Once the liquid carrier medium has been removed, crosslinking will occur, although this may take a while to develop fully, e.g. depending on criteria such as the temperature at which the curing is effected and the above-mentioned ratio of acetoacetyl groups (of the polymeric acetoacetyl compound) to the amine groups of the polyamine. As discussed supra, many of the compositions described above often cure conveniently at or near to ambient temperature, e.g. at temperatures of from 20 to 35°C, and even at temperatures down to < 0°C and are thus suitable for non-factory or on-site applications where it would be difficult to apply elevated temperatures. Of course, the compositions may also be cured at higher temperatures, e.g. 35 to 200°C, particularly :. locations where the means to apply such elevated temperatures is more convenient (as in a factory building) . The components of the compositions of the invention may in principle be supplied to the user either as "one-pack" systems, in which all the components are already formulated together (the compositions being stable and having long pot lives - often greater than 6 months in our experience) , or as "two-pack" systems in which the acetoacetyl-functional polymer(s) and the polyamine(s) are kept i separate packs until formulation is effected. The coating compositions of the invention may be employed to provide different types of coatings (e.g. protective, decorative, adhesive or sealant coatings) on a variety of substrates. They are particularly useful for providing heavy duty maintenance coatings on metal substrates such as steel. For example, they are suitable for coating steelwork structures such as bridges and industrial plants and for coating containers such as steel drums. Another particularly useful application for the coating compositions of the invention which may be mentioned is in the provision of contact adhesive compositions, especially aqueous-based, where, for example the polyamine compound is an organic polymer bearing amino groups (particularly an olefinic polymer bearing at least lateral amino groups) . Another useful application is in the form of plastisols (as discussed above) which could e.g. be used for providing underbody antichip coatings for automobiles trucks, buses and other vehicles, coil coatings, sealing gaskets for caps and closures and (when used in the form of an organosol with an added volatile organic softener) as can interior coatings. Substrates to which the compositions may be applied include metal, wood, leather, cloth, paper and plastics substrates. The coatings may be applied to the substrate by any conventional method such as by brushing, dipping, flow coating, roller coating, and spraying. The compositions of the invention may also contain other added ingredients (some of which have been mentioned above) , such as pigments, emulsifiers, surfactants, thickeners, catalysts, heat or uv stabilizers r " "-r- ' -isers, levelling agents, anti-cratering additives, fillers, fire retarαants, ant-.:-'-- agents, rheoiogy control agents, antioxidants, and other organic polymers. The present invention is now illustrated further by reference to the following examples. Unless otherwise specified all parts, percentages and ratios are on a weight basis. The term AcAc is an abbreviation for acetoacetyl. The prefix C before an example denotes that it is comparative. Measurements of Tg were effected using differential scanning calorimetry (DSC) taking the peak of the derivative curve as Tg. Measures of Mn were determined using gel permeation chromatography with a polystyrene standard. Examples Cl and 2 An acetoacetyl-functional polyester polymer was synthesised as follows: A precursor polyester polymer having hydroxyl precursor groups was prepared from the following reactants. Parts neopentyl glycol 357.5 trimethylol propane 77.5 adipic acid 96 terephthalic acid 116 isophthalic acid 353 These components were reacted at 150 to 220°C for a period of five hours until the acid value of the resulting product was about 50 mgKOH/g. 0.5 parts of the tin-based catalyst FASCAT 4101 was added (FASCAT is a registered trademark of ATOCHEM) and the polymerisation was continued until a final acid value of 5 mg KOH/g was obtained. The final hydroxyl number of the product was 110 mg KOH/g, the Tg was 14.5°C, and the Mn was 1440 g mole *1 . The precursor polyester was isolated prior to functionalisation. The hydroxyl-containing precursor polyester so obtained was then acetoacetylated by adding dropwise 232 parts of t-butyl acetoacetate to 768 parts of the polyester at 120 to 140°C over a period of four hours. The t-butanol evolved was removed under reduced pressure άistilla~ior ~ -~ resulting acetoacetylated polyester polymer was then thmneα it:. .:. - ".e to give a solution of the polyester in xylene having a solids content of 60% w/w. The degree of conversion of the available hydroxyl groups to acetoacetyl groups was shown to be 95% by 1HNMR. The AcAc functionality of the resulting polyester was 2.67. The AcAc content of the polymer was 13.8% by weight based on the weight of the polymer, and the Tg was -4.3°C. The xylene solution of the acetoacetylated polyester was then used for the formulation of pigmented coating compositions corresponding to Examples Cl and 2 using the following recipes, the composition of Example Cl being comparative and that of Example 2 being according to the invention. Example Cl Polyester solution (60% solids) 20g Ti0 2 (Kronos 2190) 12g Jeffamine T403 (triamine) 1.42g Hexane diamine 0.37g Antifoam 2 drops xylene amount to achieve solids of 60% w/w The level of Ti0 2 gives a pigment volume concentration (PVC) of approx 15%. Example 2 This formulation included methyl acetoacetate, and also benzoic acid (cure catalyst) as well as the components used in Cl. Polyester solution (60% solids) 20g Ti0 2 (Kronos 2190) 12g Jeffamine T403 (triamine) 1.42g Hexane diamine 0.37g Antifoam 2 drops Benzoic acid 0.15g Methylaceotoacetate 2.3g xylene amount to achieve solids 60% w/w In the above recipes, the amounts of polyester and polyamine used in both examples were tnose ro provide a ratio of AcAc groups in the polyester to amine groups in the polyamine of approximately 1. In Example 2, the amounts of methyl acetoacetate and polyester were those to provide a ratio of AcAc groups from the methyl acetoacetate to AcAc groups from the polyester of approximately 1. JEFFAMINE T 403 is a triamine of formula: CH 2 - (OCH J CHJ X NH J CH 3 CH 3 CH 2 C-CH 2 - (OCH 2 CH) y H 2 CH 3 CH 2 -(0CH 2 CH) z NH 2 CH 3 where x + y + z is approximately 5.3. The compositions were stored in a static air flow oven at 25°C and their stabilities assessed periodically after increasing time periods (up to 12 hours) by measuring their cone and plate viscosities (25°C) . The composition of Example Cl gelled within 1 - 4 hours while the composition of Example 2 showed slight thickening within 1 - 4 hours of adding amine but then had a stable viscosity for > 6 months. The compositions of Examples Cl and 2 were coated immediately after their formulation on chromated aluminium panels ('Bonderite 711' - Brent) and allowed to cure at 25°C for 7 days. The resulting film coatings were crosslinked as evidenced by their gel content, as determined by soxhlet extraction with tetrahydrofuran (0% gel at time zero; 74% gel after 7 days/ambient temperature) . The coated panels were placed in a QUV cabinet and exposed to UV-B (313nm peak intensity) radiation in a UV/humidity cycle (8 hours UV light, 4 hours humidity at 40°C) and run according to standard practice as described in ASTM G53-77. The 60° angle gloss of the films was recorded using a "Sheen" gloss meter. Values after radiation periods of 0, 120, and 220 hours were taken, the results being shown in the following Table 1. Table 1 Composition Normalised 60 degree gloss used retention 0 hr 120 hr 260 hr Ex.Cl 100% 37% 20% Ex.2 100% 110% 86% Examples C3 to C5. 6 to 9, CIO, Cll In this example, the effect of varying the ratio of the number of AcAc groups from methyl acetoacetate to the number of AcAc groups from a polyester was investigated. The polyester used was that employed in Examples Cl and 2 and the formulation employed was that for Example Cl apart from using different amounts of methyl acetoacetate to vary the above-ment oned ratio from 0/1 (i.e. no methyl acetoacetate employed) to 2/1. The times to gel were recorded (see Table 2) . The compositions 7 to 9, CIO, Cll were also coated immediately onto shot blasted mild steel panels (primed with a 40-50 μm dry film thickness zinc phosphate primer) and their touch dry behaviour observed (see Table 2) . Table 2 Ex. Ratio of Time to gel Touch dry (td) NO. AcAc groups behaviour at ambient temp. C3 0/1 2 hours C4 0.5/1 <24 hours C5 0.66/1 <24 hours 6 0.8/1 3 weeks 7 0.9/1 several months td within 1 day 8 1.0/1 >1 year td within 1 day 9 1.5/1 >l year td with 1 week CIO 2.0/1 >1 year still tacky after 1 month Cll 3/1 >i year still tacky after 1 month It will be noted that the onset ratio for a significant improvement in pot life was 0.8/1. Further, although formulations with ratios above 1.5/1 were storage stable, they were exceedingly slow in becoming touch dry, indicating a very slow cure rate and impairment of coating properties. Examples C12, 13, 14, and C15 In these Examples, the effect of varying the number of carbon atoms in the alkyl group of the alkyl acetoacetyl compound was investigated. A precursor polyester polymer was prepared as per the procedure used for the polyester of Examples Cl and 2, except that the following recipe was employed. Parts neopentyl glycol 431.6 trimethylol propane 61.6 adipic acid 243.8 terephthalic acid 61.4 isophthalic acid 353.6 The product had an acid value of 4.0 mg KOH/g, a hydroxyl number of 78.4 mg KOH/g, a Tg of 4.7°C, and a Mn of 1960 g mole "1 The hydroxy-containing precursor polyester so obtained was then acetoacetolytated using t-butyl acetoacetate as per the procedure used in Examples Cl/2 except that 273 parts of t-butyl acetoacetate were used. The resulting acetoacetylated polymer was thinned with xylene to give a solution of solids 60% w/w. The degree of conversion of the available hydroxyl groups to acetoacetyl groups was shown to be 98% by NMR. Tg was -16.3°C. The AcAc content of the polymer was 12.3% by weight based on the weight of the polymer. The polyester solution (60% w/w in xylene) was then, in separate examples, formulated with Jeffamine T403 (amount to provide a ratio of AcAc groups in the polyester to amine groups in the polyamine of 1/1) and a monoacetoacetyl compound (see following Table 3) (ratio of AcAc groups from the monoacetoacetyl compound to AcAc groups from the polyester 1/1) . The times to gel were recorded (see Table 3) . Table 3 Ex. monoacetoacetyl Time to gel No. compd. used 12 acetoacetic acid gelled < 24 hours 13 methyl acetoacetate stable > 1 month 14 ethyl acetoacetate stable > 1 month C15 t-butyl acetoacetate gelled < 24 hours It will be noted that only selected monoacetoacetyl compounds within the scope of the invention resulted in a significant improvement in storage stability. Examples C16 and 17 A low molecular weight acrylic polymer (Mn = 1093) was prepared using conventional solution polymerisation in xylene from the monomers methyl methacrylate (MMA) and acetoacetoxyethyl methacrylate (AAEM) having the composition MMA/AAEM - 75.5/24.5 w/w (Tg = 24.7°C and solution viscosity at 50% w/w solids in xylene = 1.9 poise) . Formulations corresponding to Examples C16 and 17 (with and without methyl acetoacetate) were prepared as follows. Ex C16 (g) Ex 17 (g) acrylic polymer (50% w/w) 17 35 Jeffamine T403 1.47 2.94 methyl acetoacetate 0 2.36 benzoic acid 0 0.3 The composition of C17 and 18 were cast 24 μm wet onto chromated aluminium panels. Properties of the resulting coatings, and the storage stability of the compositions, are shown in the following Table 4. Table 4 17 Touch dry time 30 min 1 hour Storage stability gelled < 24 hr stable > 1 month Time to loss of 50% 240 hr 330 hr gloss at 60° angle (QUV (B) )

Claims: CLAIMS 1. A crosslinkable liquid carrier-based coating composition formulated from components comprising an organic polymer(s) having acetoacetyl group functionality, a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, and a non- polymeric monoacetoacetyl compound(s) which can evaporate on coating formation selected from at least one of alkyl acetoacetate, alkyl acetoacetamide and 1-alkyl-l,3-butanedione where said alkyl groups in said compounds have from 1 to 3 carbon atoms, and wherein the ratio of the number of acetoacetyl groups from said monoacetoacetyl compound(s) to the number of polymer-bound acetoacetyl groups from said organic polymer(s) having acetoacetyl group functionality is within the range of from 0.8/1 to 1.5/1. 2. A composition according to claim 1 wherein the ratio of the number of acetoacetyl groups from said monoacetoacetyl compound(s) to the number of polymer-bound acetoacetyl groups is within the range of from 0.8/1 to 1.2/1. 3. A composition according to either claim 1 or claim 2 wherein said composition is organic liquid-based. 4. A composition according to either claim 1 or claim 2 wherein said composition is water-based. 5. A composition according to any one of the preceding claims wherein said polymer-based acetoacetyl groups are provided by acetoacetate groups of formula 0 0 II II CH— -CH, -C-0- or by acetoacetamide groups of rcrrr.ula 0 O R 1 CH 3 -C «-C -H 2 --it- wherein R 1 is hydrogen or a monovalent hydrocarbyl radical. 6. A composition according to any one of the preceding claims wherein the acetoacetyl content of said organic polymer is from 1 to 50% by weight of the polymer. 7. A composition according to any one of the preceding claims wherein said organic polymer(s) having acetoacetyl functionality is selected from the group consisting of polyester polymers, polyurethane polymers and addition polymers of olefinically unsaturated monomers. 8. A composition according to any one of the preceding claims wherein said organic polymer having acetoacetyl functionality is a polyester having an acetoacetyl content of from 3 to 50 weight % 'based on polymer weight and a glass transition temperature of from -40 to 120°C. 9. A composition according to any one of the preceding claims wherein said non-polymeric monoacetoacetyl compound is selected from methyl acetoacetate, ethyl acetoacetate, methyl acetoacetamide, ethyl acetoacetamide, and acetyl acetone. 10. A composition according to Claim 9 wherein said monoacetoacetyl compound is selected from methyl acetoacetate and ethyl acetoacetate. 11. A composition according to any one of the preceding claims wherein the ratio of the number of acetoacetyl groups of the acetoacetyl functional polymer(s) to the number of acetoacetyl- reactive amino groups of the polyamine compound(s) is within the range of from 0.5/1 to 2/1. 12. A composition according to any one of the preceding claims which composition includes an aci: catalyst for the cure reaction between the polymer-based acetoacetyl groups and the polyamine after coating formation. 13. Method of preparing a crosslinkable liquid carrier-based coating composition which method comprises formulating components which comprise an organic polyme (s) having acetoacetyl functionality, a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, and a non-polymeric monoacetoactyl compound(s) which can evaporate on coating formation selected from at lest one of alkyl acetoacetate, alkyl acetoacetamide and 1-alkyl-l,3-butaneione where said alkyl groups in said compounds have from 1 to 3 carbon atoms, wherein the ratio of the number of acetoacetyl groups from said monoacetoacetyl compound(s) to the number of polymer-bound acetoacetyl groups from said organic polymer(s) having acetoacetyl group functionality is within the range of from 0.8/1 to 1.5/1. 14. Use of a coating composition according to any one of claims 1 to 12 for the provision of a crosslinked coating on a substrate. 15. Use according to claim 14 wherein said use is for the provision of a maintenance coating on a metal substrate, or a contact adhesive, or a plasticised coating. 16. A crosslinked coating derived from a coating composition according to any one of claims 1 to 12. 17. A crosslinked coating according to claim 16 which is in the form of a maintenance coating on a metal substrate, or a contact adhesive, or a plasticised coating.

Inventors: BROWN RICHARD ANDREW, PADGET JOHN CHRISTOPHER, THOMAS MARK, YEATES STEPHEN GEORGE, BROWN, RICHARD, ANDREW, PADGET, JOHN, CHRISTOPHER, THOMAS, MARK, YEATES, STEPHEN, GEORGE
Applicants: BROWN RICHARD ANDREW, PADGET JOHN CHRISTOPHER, THOMAS MARK, YEATES STEPHEN GEORGE, ZENECA LTD, BROWN, RICHARD, ANDREW, PADGET, JOHN, CHRISTOPHER, THOMAS, MARK, YEATES, STEPHEN, GEORGE, ZENECA LIMITED
Application year: 1994
Main classification: C09D201
IPC codes: C08F8, C08G18, C08G63, C09D133, C09D167, C09D201